A variety of unusual responses (hypo- and hyper-responses) to sensory stimuli are documented in children with autism and appear to be exacerbated in social situations. The developmental nature of these phenomena and their relationship to the core features of autism are not well understood. Our model explaining unusual sensory experiences in autism involves a basic deficit in information processing (sensory orienting), moderated by social context and development. The specific aims of this project are to: (1) measure developmentally-related changes in responses to sensory experiences in young children with autism, children with other developmental disabilities (DD), and typically-developing children; (2) identify sensory processing patterns that are unique to autism; and (3) determine the extent to which sensory processing patterns covary with phenotypic expressions of autism. A cross-sectional methodology will be used to study unusual sensory experiences in 180 children (60 with autism, 60 with DD, and 60 with typical development). The autism and DD groups will range from 2-7 years of age. All three groups will be matched according to nonverbal mental age and gender. Children will be assessed using a battery of measures (diagnostic, developmental, sensory, and phenotypic features). A cross-sectional methodology will test the degree to which frequencies of sensory symptoms vary as a function of maturational variables and group membership. Composite scores reflecting four sensory processing patterns (hypo/hyper-responsiveness to social/nonsocial stimuli) will be analyzed to specifically discriminate autism from other groups. Finally, these sensory patterns will be correlated with measures of social-relatedness, communication, and restricted/repetitive behaviors. Our conceptual model predicts that a) all three groups will demonstrate a decrease in unusual responses to sensory stimuli as age, cognitive abilities, and language increase, b) the autism group will have the highest frequency of symptoms, c) a hypo-responsive pattern (orienting deficit) will be specific to autism, magnified for social versus nonsocial stimuli, and d) the four patterns of sensory processing will differentially correlate with social-relatedness subtypes and levels of severity in the phenotypic characteristics of autism.